Fyrestrike

Agreed, I think we can safely say that the piston indeed did melt but that does not explain the fracture on the sleeve (I'll get a better pic). There is melted piston material scattered on the top of the piston and some on the head between the valve and the cylinder boundary.

Sideways

It appears to be too agressive with the tune. Pre-ignition takes out the plug that takes out everything else.

cbender

I'm assuming you've got a wideband but (based on what's been said earlier in this thread) you weren't datalogging at the time. What sort of air-fuel ratios have you been targetting, what does your AEM timing map look like at those boost-rpm combo's, and did the engine grenade at a boost transition -- or at steady WOT?

CB -- once turbo'd now thankfully NA

Fyrestrike

The car uses a 1052U unit but does not have a gauge hooked up. On the dyno we were seeing ~12:1 A/F ratio so it wasn't too lean. The engine definetely let go at WOT and max RPM.

The problem seems to be that the adaptive boost map was not used. The peak hold function of the boost gauge is showing us that the car hit almost 12psi since it was so cold that weekend. The car has a stock MAP sensor which only reads to 10.94. The car was only tuned up to 9psi so if it hit 12psi then it was using the same fuel/timing values which would surely cause detonation/lean condition. I guess even if we had a 3bar map sensor, that the tune was never made to run any higher than 9psi

RWD_RCKT

How can a SC gain 3psi from weather?! I could see it gaining a little from Thermodynamic efficiency... but 33%????

Dumb question, but is the gauge good?

RWD_RCKT

Or was this a 9psi at 9k... 12psi at 9700RPM thing?

Eugeneo

Could it have been a plugged or fouled injector causing a lean condition only in that cyl?

Fyrestrike

Remember that it was 9psi@9000 but in the top speed run it was spinning as fast as the AEM would let it which was 9700 which means it was making almost 12psi.

The gauge is a Defi, I doubt it's bad.

Sideways

What was the total degrees of advance at 9500 rpm?

cbender

Just a shot in the dark, but I'd guess one the following:

1. Inadequate fuel and/or excessively advanced timing either b/c (i) the fuel and timing values above 9psi in your AEM maps are inappropriate (you said you'd tuned the car only up to 9psi) or (ii) the air-fuel mixture went lean once you exceeded 10.94 psi so the AEM was supplying fuel and running timing for less boost (by a full psi) than you were actually running.

2. You exceeded the capacity of the injectors to provide enough fuel either b/c (i) one injector got partially clogged (it happens) or (ii) you exceeded the maximum injector duty cycle by virtue of trying support a full 12psi of boost.

Btw, I often had boost spikes well beyond the boost ceilings in my AEM, but they were mostly very short in duration. I attributed it to the difficulty of the wastegate responding quickly enough during periods where boost was ramping quickly.

Finally, when you compress very cold air, wouldn't you expect leaner air-fuel mixtures simply by virtue of the fact that you've got denser air (this is where my command of the chemistry/physics fails me, but just a thought).

In any event, sorry to hear of your misfortune.

CB